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PROCESSING
A new technology
based on the adiabatic
cooling of swirling gas
flow in a supersonic
nozzle is effective in sepGas Processing
arating and processing
natural gas components.
A pilot test facility in Alberta, Canada, has shown that the 3-S separation
device uses 10-20% less compressor
power than plants that use a JouleThomson valve or turboexpander, based
on the same extraction level.
Potential applications for 3-S separators in gas processing plants include:
• Gas preparation for transportation.
• LPG extraction, shallow cut, and
deep cut.
• Offshore gas separation and treatment facilities.
• CO2 extraction, ethane recovery,
and LNG applications.
3-S separators provide a cost-effective and highly efficient extraction process for C3+ gas components combined
with a potential reduction in energy
consumption.
temperatures are based on the JouleThomson effect and use of gas-expansion equipment. The gas processing
industry developed and has used them
extensively.
Recent research has produced new
technologies based on adiabatic cooling, which results from gas expansion in a supersonic nozzle. Cryogenic
temperatures result because part of gas
Supersonic nozzle efficiently
separates natural gas components
enthalpy transforms to kinetic energy,
which can be reused to increase the
pressure in the system of supersonic
and subsonic diffusers.
The nozzle’s working section liquefies target components. It experiences
significantly lower pressures and temperatures than would occur at the facility exit without the addition of external
energy.
Laval nozzle
Fig. 1 compares the degree of natural
Existing approaches to obtaining low gas cooling at the same differential
N ATURAL GAS COOLING
Vadim Alfyorov
Lev Bagirov
Leonard Dmitriev
Vladimir Feygin
Salavat Imayev
TransLang Technologies Ltd.
Moscow
John R. Lacey
TransLang Technologies Ltd.
Calgary
Fig. 1
70
T 1 = 290 K
P 1 = 40 atm
60
Temperature difference, K
Laval nozzle device
50
40
Turboexpander
30
20
Joule-Thomson valve
10
0
1
2
3
4
Pressure ratio, P1/P2
5
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PROCESSING
3-S SEPARATOR
Fig. 2
Supersonic nozzle
Swirling device
pressure for a Joule-Thomson valve,
turboexpander, and the new device that
uses a Laval nozzle.
For the Laval nozzle, we assume that
∆T = ∆Tst = T1 – Tst, where T1 is the input gas temperature and Tst is the static
temperature of gas after its expansion.
The output pressure, P2, after flowing through the system of diffusers is
assumed to be two times smaller than
a respective pressure P2 in supersonic
wind tunnels at the same Mach number.
Fig.1 shows that natural gas expan-
Two-phase separator
Working suction
sion in the Laval nozzles and subsequent pressure increase in the system
of diffusers allow one to obtain a ∆Tst
that exceeds the temperature difference
∆T in expanders at the same differential
pressure.
Supersonic separation
technologies
The supersonic nozzle separates
drops of condensed liquid using centrifugal forces, which are formed by
two different methods. The swirling
The pilot device, designed for long service, was constructed in Calgary (Fig. 3).
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Directing vanes
Supersonic, subsonic
difffusers
(twisting) device can be at the outlet of
the supersonic nozzle or the gas flow is
swirled in the plenum chamber ahead
of the supersonic nozzle.
Twister BV, Rijswijk, Netherlands, has
developed a product that uses the first
method.1 2 A wing or blade at the end of
the nozzle in the supersonic flow zone
immediately before the liquid extraction device provides swirling to the gas
passing through the device. The Twister
separator dehydrates gas and separates
heavy hydrocarbons.
This approach to create flow swirling
forms a shock wave that heats the gas,
creates pressure losses, and creates subsonic flow zones in the separation area.
As the flow decelerates, the shock wave
produces partial crushing and evaporation of the drops of liquid.
The second method, using a swirling
device in the plenum chamber ahead of
the nozzle, was independently proposed
by a group of Russian specialists and
developed with their participation by
TransLang Technologies Ltd., Calgary.
This method initiates gas swirling
in the plenum chamber so that the
tangential velocities, when combined
with the centrifugal forces, separate any
liquid drops formed in the supersonic
nozzle and deliver them to a special
extracting device.
This approach minimizes total
pressure losses in the shock waves and
Oil & Gas Journal / May 23, 2005
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3-S technology studies
3-S separators have been studied
and tested since 1996. Experimental
laboratories were constructed to fully
analyze the process of drop formation
in supersonic flows. In addition to the
pattern of swirling supersonic flows,
researchers determined drop distribution functions along the nozzle radius
and length, and also developed optical
methods to measure drop sizes.
Chromatographic procedures were
modified to apply to experimental conditions. The calculation programs for
swirling natural gas flows in supersonic
nozzles were elaborated to give due
recognition to actual gas properties and
phase transitions.
The desire to optimize the design
for industrial 3-S separator applications led to construction in Russia of
an experimental test plant providing
natural gas flow rates of 1.2-2.5 kg/sec
at the plenum chamber entry with pressures up to 75 atm. The temperature of
gas varied from 20° to –60° C. with an
F
3-S EFFECTIVENESS
Fig. 4
0.7
0.6
3-S effectiveness, ∆α, mole %
separates the flow deceleration zone
behind the shock wave from the drop
separation zone.
This method of flow swirling is
called 3-S technology (supersonic separation) and the devices designed with
this technology are called 3-S separators.3 4
Fig. 2 shows a 3-S separator.
Its distinctive feature is the arrangement of the swirling device in the plenum chamber. This is followed by the
supersonic nozzle, the working section,
the device for separating two-phase
flow with liquefied components, the
supersonic and subsonic diffusers, and
finally the directing vanes.
Different types of devices are used
to achieve flow swirling that gives a
centrifugal force with an acceleration
of about 106 m/sec2 in the supersonic
nozzle and the working section. The
devices include blades on the central
body and one or more gas jets along the
tangent to the surface of the nozzle entry section. These options allow optimal
design for this section of the device.
0.5
Equal efficiency
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
Joule-Thomson effectiveness, ∆α, mole %
3-S SEPARATOR FLOW SCHEME
Evaporator
Fig. 5
3-S separator
Feed
gas
Secondary
separator
C 3+
E XTRACTION EFFICIENCY
Fig. 6
100
80
C3+ extraction, %
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JOURNAL
60
3-S separator
Turboexpander
40
Joule-Thomson
20
0
–40
–30
–20
–10
0
Post-chiller gas temperature, °C.
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PROCESSING
J OULE-THOMSON FLOW SCHEME
Fig. 7
Joule-Thomson
valve
Evaporator
Separator
Feed
gas
Exchanger
Separator
C3+
T URBOEXPANDER FLOW SCHEME
Fig. 8
Turboexpander
Evaporator
Separator
Feed
gas
Liquid
condensate
Exchanger
Compressor
Separator
C 3+
exhaust pressure of 15-60 atm.
The test plant can measure gas flow
rates at different points in the 3-S
device, pressures along the entire gas
flow path channel, and gas temperatures in different parts of the test device.
Furthermore, it allows chromatographic
analyses of gas composition. The test
plant is equipped with special devices
to supply a specified gas composition.
Target component removal determines the 3-S separator’s effectiveness.
Currently more than 400 test runs in
this test plant have investigated the operation of various design versions of the
3-S separator and its components.
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The next stage included the design
and manufacture of a pilot plant with a
greater natural gas flow rate, up to 12
kg/sec, at an inlet pressure of 50-70
atm. This plant, designed for extended
periods of service was built in Calgary
(Fig. 3).
A range of experimental investigations was conducted up to those
approaching industrial applications.
Experimental results confirmed the preliminary results and conclusions from
the laboratory test device.
The first industrial 3-S device has
recently started operating at a gas-treatment plant in Western Siberia.
From the data obtained from these
test facilities, mathematical programs
were developed to calculate the 3-S
separator physical components under
different operating conditions.
Fig. 4 shows the results of a series of
test runs carried out in the pilot plant
at a gas flow rate of 1.5-2.5 kg/sec.
The separation effectiveness for heavier
components in the 3-S separator is plotted on the vertical axis and the effectiveness of the Joule-Thomson valve is
on the horizontal axis.
The separation effectiveness is
measured with ∆a = a0 − a, where
a0 and a are the initial and final mole
concentrations of components.
The tests used different feed component concentrations, entry-gas pressures
and temperatures, differential pressures,
and gas dynamic flow conditions. The
results are for Mach numbers less than
1.5 in the 3-S separator working section.
The separation efficiency in the 3-S
separator slightly decreases with an
increase of heavy components. This is
due to the characteristics of thermodynamic expansion of mixtures with high
concentrations of heavy components;
for these types of mixtures, the appearance of liquid in the separator premix
chamber is normal.
For certain conditions, especially
with small concentrations of heavier
hydrocarbons, the 3-S separator can
separate liquid components that a JouleThomson valve could not.
Comparison with existing
technologies
At the same differential pressure, the
3-S separator can achieve considerably
lower temperatures in the liquid separation section due to adiabatic cooling
during expansion in the supersonic
nozzle and the Joule-Thomson effect.
We compared the effectiveness of the
3-S separator, Joule-Thomson valve, and
turboexpander in extracting C3+ from
natural gas.
Fig. 5 shows a diagram of a facility with 3-S separator and the chiller
to extract C3+ from natural gas. In this
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O FFSHORE 3-S APPLICATION
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Fig. 9
Condensate extraction
3-S separator
Gas
pipeline
Exchanger
Gas-liquid
separator
Wellhead
Sea bottom
Condensate
preparation for
pipelining
Condensate
pipeline
Well
facility, natural gas is supplied to the 3-S
separator after cooling in the recuperative heat exchanger and evaporator.
Gas from the 3-S separator flows to
the recuperative heat exchanger, which
cools the feed gas. Two-phase flow from
the 3-S separator flows to the secondary separator, the gas phase of which
mixes with purified flow from the 3-S
separator.
Fig. 6 shows the extraction of C3+
from natural gas and its dependence on
the stream temperature after the evaporator. The feed gas temperature was 20°
C. and the feed gas composition was
methane, 90 mole %; ethane, 2 mole
%; propane, 4 mole %; and butanes, 4
mole %.
The gas pressure at the entry and exit
was 60 atm and 45 atm, respectively.
Projected flow separation in the 3-S
separator was based on the experimental data obtained during the tests of
pilot industrial 3-S separators.
Fig. 6 also shows C3+ extraction for a
Joule-Thomson valve or turboexpander.
Figs. 7 and 8 show flow schemes for
a Joule-Thomson valve and turboexpander, respectively.
Fig. 6 assumes that the isentropic turbine efficiency is 80% and the
isentropic turboexpander compressor
efficiency is 75%. Pressure losses, temperature approaches, and pressure losses
in the recuperative heat exchanger are
the same for all schemes.
The 3-S separator results in a higher
extraction of C3+ vs. the Joule-Thomson valve and turboexpander. The 3-S
separator is simpler to design, operate,
and maintain.
Advantages in field plants
Gas processing plants with the 3-S
separator have:
• Fewer compressor station power
requirements.
• Lower pressure loss.
• Greater recovery given the same
operating parameters.
• A simpler plant design.
• Fewer moving parts.
• Ease of construction and reduction
in plant weight.
• Lower equipment, operating, and
maintenance costs.
Calculations based on experimental data for particular fields show that
using the 3-S technology results in a
30% increase in the recovery of heavier
gas components for the same power
requirements. For the same extraction
level, the power requirement could be
reduced 50-70%.
Using 3-S separators instead of
Joule-Thomson valves in existing gas
processing and extraction plants increases LPG extraction 10-20% with the
same compressor power. For the same
extraction level, it is possible to de-
crease the required compressor power
by 10-20%.
At gas processing plants equipped
with turboexpanders and coolers, using
3-S extractors could lead to a 15-20%
reduction in the required compressor
power at the same extraction level.
Offshore example
Because the 3-S technology has a
small footprint, has no moving parts,
needs no maintenance personnel, and
uses the gas formation’s energy, the
capital and operating costs are lower vs.
conventional gas processing plants.
These factors make the 3-S technology especially promising for offshore
fields. Most gas production platforms
limit the gas pressure to 100 atm for
safety reasons. Wellhead gas pressures
often exceed 100 atm, which results in
the need for a Joule-Thomson valve to
reduce the gas pressure.
Replacing the Joule-Thomson valve
with a 3-S separator solves several problems: pressure reduction, gas dehydration, LPG extraction, and dewpoint
control.
Fig. 9 shows a possible scheme using
a 3-S separator for LPG extraction in an
offshore gas field.
Gas from the well, after passing the
wellhead, flows to the processing facility with the 3-S separator mounted near
the wellhead. The facility consists of a
Oil & Gas Journal / May 23, 2005
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Glossary of the
Petroleum Industry:
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Encompassing more than 20,000
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Included are many new technical and
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recuperative heat exchanger, a 3-S separator, and a secondary separator.
The liquid mixture of hydrocarbons
and water separated from the natural
gas flow to a special facility to prepare
condensate for transportation. The effectiveness of the separation process
is comparable with schemes that use a
turboexpander. ✦
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holds a degree (1963) in physics from the Moscow Institute of Physics and Technology.
Vladimir Feygin (engo@orc.ru) is a director of
TransLang Technologies Ltd., Moscow. He has also
served as an executive director of ENGO Research
Center since 1990. In 1970-2004, Feygin was a
researcher at Gazprom’s institute, Niigazekonomika. He holds a degree (1967) and a PhD (1971)
in mathematics from Moscow State University.
Salavat Imaev (imaevsalavat@netscape.net) is
deputy director of the fundamental aspects of oil
References
and gas science and technology department at the
1. Cottrll, A. “Technique puts gas
Moscow Institute of Physics and Technology. He
treatment in a spin,” Upstream, Mar. 19, holds a degree (1993) and a PhD (1998) in
physics and mathematics from the Moscow Insti2004, p. 48.
tute of Physics and Technology.
2. Okimoto, F., and Brouwer, J.,
“Supersonic gas condition,” World Oil, John R. Lacey (drjohnl@irlacey.com) is presiAugust 2002.
dent of of John R. Lacey International Ltd. and
3. Alferov, V.I., et al., “Method and
chairman of TransLang Technologies Ltd., Calgary.
He has advised on major oil and gas developments
apparatus for liquefying a gas,” Euroand transmission projects around the world. Before
pean Patent, EP1131588.
his own company in 1970, Lacey worked
4. Alferov, V.I., et al., “Method of and forming
for BP Canada for 15 years. He holds a BSc
apparatus for the separation of compo- (1953) in petroleum technology from the Royal
nents of gas mixtures and liquefaction
School of Mines, London, and a PhD (1955) in
geology from the University of London. Lacey was
of a gas,” US Patent 6372019.
elected to the Russian Academy of Natural Sciences
in 1996 and is Honourary Consul-General for the
Kingdom of Thailand.
The authors
Vadim Alfyorov (wtdiv@tsagi.ru) is a director of
TransLang Technologies Ltd., Moscow. He is also
division head of the Central Aerohydrodynamic
Institute, where he has worked since 1958. Since
1987, Alfyorov has served as a professor at the
department of Flying Machines of the Moscow
Institute of Physics and Technology. He holds a
degree (1957) and a PhD in physics from the
Moscow Institute of Physics and Technology. He is
a member of the American Institute of Aeronautics
and Astronautics and is an Honoured Scientist of
the Russian Federation.
Lev Bagirov (engo@orc.ru) is a director of
TransLang Technologies Ltd., Moscow. He has
also been a director of new technologies for the
ENGO Research Center since 1998. Before that,
Bagirov served as a senior scientist in the Institute
for Problems in Mechanics, Russian Academy of
Sciences. He holds a degree (1966) and a PhD
in mathematics (1970) from Moscow State
University.
Leonard Dmitriev is a chief engineer for TransLang
Technologies Ltd. and senior research scientist at
the Central Aerohydrodynamic Institute, Moscow,
specializing in applied aspects of gas dynamics. He
has worked at the institute since 1964. Dmitriev
Oil & Gas Journal / May 23, 2005
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